Heat pump water heater appliance and a method for operating a heat pump water heater appliance

ABSTRACT

A method for operating a water heater appliance includes establishing a standby recovery temperature for the heat pump water heater appliance based at least in part on a set temperature of the heat pump water heater appliance and activating a sealed system of the heat pump water heater appliance if a temperature measurement from a tank temperature sensor is less than the standby recovery temperature. An ambient temperature may also be used to establish the standby recovery temperature for the heat pump water heater appliance. A related water heater appliance is also provided.

FIELD OF THE INVENTION

The present subject matter relates generally to water heater appliances, such as heat pump water heater appliances.

BACKGROUND OF THE INVENTION

Water heater appliances generally operate to heat water within tanks of the water heater appliances to a predetermined set temperature. Various heating elements are available to heat water within water heater appliances. For example, electric water heaters utilize electric heating elements to heat water, gas water heaters utilize gas burners to heat water, and heat pump water heaters utilize a sealed heat pump system to heat water.

Generally, water heater appliances heat water to the predetermined set temperature and then deactivate the heating elements for a period of time. While the heating elements are deactivated, water within the water heater appliances may cool. The water heater appliances generally permit the water to cool to a few degrees below the predetermined set temperature and then reactivate the heating elements to bring the temperature of the water back up to the predetermined set temperature. In heat pump water heaters, such cycling can have various drawbacks. In particular, frequently starting and stopping a compressor of the sealed heat pump system can excessively wear the compressor. In addition, short cycling the compressor can negatively affect an efficiency of the sealed heat pump system due to transient losses.

Accordingly, methods for operating a heat pump water heater appliance that assist with limiting or preventing short cycling of a sealed heat pump system of the heat pump water heater appliance would be useful. In particular, methods for operating a heat pump water heater appliance that assist with limiting or preventing short cycling of a sealed heat pump system of the heat pump water heater appliance while also providing adequate heated water to a user of the heat pump water heater appliance would be useful.

BRIEF DESCRIPTION OF THE INVENTION

The present subject matter provides a method for operating a water heater appliance. The method includes establishing a standby recovery temperature for the heat pump water heater appliance based at least in part on a set temperature of the heat pump water heater appliance and activating a sealed system of the heat pump water heater appliance if a temperature measurement from a tank temperature sensor is less than the standby recovery temperature. An ambient temperature may also be used to establish the standby recovery temperature for the heat pump water heater appliance. A related water heater appliance is also provided. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In a first exemplary embodiment, a method for operating a heat pump water heater appliance is provided. The method includes determining a set temperature of the heat pump water heater appliance, measuring an ambient temperature about the heat pump water heater appliance with an ambient temperature sensor of the heat pump water heater appliance, establishing a standby recovery temperature for the heat pump water heater appliance based at least in part on the set temperature of the heat pump water heater appliance and the ambient temperature about the heat pump water heater appliance, receiving a temperature measurement from a tank temperature sensor of the heat pump water heater appliance during a standby operation of the heat pump water heater appliance, and activating a sealed system of the heat pump water heater appliance if the temperature measurement from the tank temperature sensor is less than the standby recovery temperature at the step of receiving.

In a second exemplary embodiment, a heat pump water heater appliance is provided. The heat pump water heater appliance includes a tank that defines an interior volume. The heat pump water heater appliance also includes an ambient temperature sensor. A tank temperature sensor is positioned at the tank and is configured for measuring a temperature of water within the interior volume of the tank. A sealed system is operable to heat water within the interior volume of the tank. The sealed system has a compressor. A controller is in operative communication with the ambient temperature sensor, the tank temperature sensor and the compressor of the sealed system. The controller is configured for measuring an ambient temperature with the ambient temperature sensor, establishing a standby recovery temperature based at least in part on a set temperature and the ambient temperature, receiving a temperature measurement from the tank temperature sensor during a standby operation, and activating the compressor of the sealed system if the temperature measurement from the tank temperature sensor is less than the standby recovery temperature at the step of receiving.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures.

FIG. 1 provides a perspective view of a water heater appliance according to an exemplary embodiment of the present subject matter.

FIG. 2 provides a schematic view of certain components of the exemplary water heater appliance of FIG. 1.

FIG. 3 illustrates a method for operating a water heater appliance according to an exemplary embodiment of the present subject matter.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 provides a perspective view of a water heater appliance 100 according to an exemplary embodiment of the present subject matter. FIG. 2 provides a schematic view of certain components of water heater appliance 100. Water heater appliance 100 includes a casing 102. A tank 112 (FIG. 2) is mounted within casing 102. Tank 112 defines an interior volume 114 for heating water therein.

Water heater appliance 100 also includes a cold water conduit 104 and a hot water conduit 106 that are both in fluid communication with tank 112 within casing 102. As an example, cold water from a water source, e.g., a municipal water supply or a well, enters water heater appliance 100 through cold water conduit 104. From cold water conduit 104, such cold water enters interior volume 114 of tank 112 wherein the water is heated to generate heated water. Such heated water exits water heater appliance 100 at hot water conduit 106 and, e.g., is supplied to a bath, shower, sink, or any other suitable feature.

As may be seen in FIG. 1, water heater appliance 100 extends between a top portion 108 and a bottom portion 109 along a vertical direction V. Thus, water heater appliance 100 is generally vertically oriented. Water heater appliance 100 can be leveled, e.g., such that casing 102 is plumb in the vertical direction V, in order to facilitate proper operation of water heater appliance 100.

A drain pan 110 is positioned at bottom portion 109 of water heater appliance 100 such that water heater appliance 100 sits on drain pan 110. Drain pan 110 sits beneath water heater appliance 100 along the vertical direction V, e.g., to collect water that leaks from water heater appliance 100 or water that condenses on an evaporator 128 of water heater appliance 100. It should be understood that water heater appliance 100 is provided by way of example only and that the present subject matter may be used with any suitable water heater appliance.

Turning now to FIG. 2, water heater appliance 100 includes an upper heating element 118, a lower heating element 119 and a sealed system 120 for heating water within interior volume 114 of tank 112. Thus, water heater appliance 100 is commonly referred to as a “heat pump water heater appliance.” Upper and lower heating elements 118 and 119 can be any suitable heating elements. For example, upper heating element 118 and/or lower heating element 119 may be an electric resistance element, a microwave element, an induction element, or any other suitable heating element or combination thereof. Lower heating element 119 may also be a gas burner.

Sealed system 120 includes a compressor 122, a condenser 124, a throttling device 126 and an evaporator 128. Condenser 124 is thermally coupled or assembled in a heat exchange relationship with tank 112 in order to heat water within interior volume 114 of tank 112 during operation of sealed system 120. In particular, condenser 124 may be a conduit coiled around and mounted to tank 112. During operation of sealed system 120, refrigerant exits evaporator 128 as a fluid in the form of a superheated vapor and/or high quality vapor mixture. Upon exiting evaporator 128, the refrigerant enters compressor 122 wherein the pressure and temperature of the refrigerant are increased such that the refrigerant becomes a superheated vapor. The superheated vapor from compressor 122 enters condenser 124 wherein it transfers energy to the water within tank 112 and condenses into a saturated liquid and/or high quality liquid vapor mixture. This high quality/saturated liquid vapor mixture exits condenser 124 and travels through throttling device 126 that is configured for regulating a flow rate of refrigerant therethrough. Upon exiting throttling device 126, the pressure and temperature of the refrigerant drop at which time the refrigerant enters evaporator 128 and the cycle repeats itself. In certain exemplary embodiments, throttling device 126 may be an electronic expansion valve (EEV).

Water heater appliance 100 also includes a tank temperature sensor 130. Tank temperature sensor 130 is configured for measuring a temperature of water within interior volume 114 of tank 112. Tank temperature sensor 130 can be positioned at any suitable location within or on water heater appliance 100. For example, tank temperature sensor 130 may be positioned within interior volume 114 of tank 112 or may be mounted to tank 112 outside of interior volume 114 of tank 112. When mounted to tank 112 outside of interior volume 114 of tank 112, tank temperature sensor 130 can be configured for indirectly measuring the temperature of water within interior volume 114 of tank 112. For example, tank temperature sensor 130 can measure the temperature of tank 112 and correlate the temperature of tank 112 to the temperature of water within interior volume 114 of tank 112. Tank temperature sensor 130 may also be positioned at or adjacent top portion 108 of water heater appliance 100, e.g., at or adjacent an inlet of hot water conduit 106.

Tank temperature sensor 130 can be any suitable temperature sensor. For example, tank temperature sensor 130 may be a thermocouple or a thermistor. As may be seen in FIG. 2, tank temperature sensor 130 may be the only temperature sensor positioned at or on tank 112 that is configured for measuring the temperature of water within interior volume 114 of tank 112 in certain exemplary embodiments. In alternative exemplary embodiments, additional temperature sensors may be positioned at or on tank 112 to assist tank temperature sensor 130 with measuring the temperature of water within interior volume 114 of tank 112, e.g., at other locations within interior volume 114 of tank 112.

Water heater appliance 100 also includes an ambient temperature sensor 132. Ambient temperature sensor 132 is configured for measuring a temperature of air about water heater appliance 100. Ambient temperature sensor 132 can be positioned at any suitable location within or on water heater appliance 100. For example, ambient temperature sensor 132 may be mounted to casing 102, e.g., at or adjacent top portion 108 of water heater appliance 100. Ambient temperature sensor 132 can be any suitable temperature sensor. For example, ambient temperature sensor 132 may be a thermocouple or a thermistor.

Water heater appliance 100 further includes a controller 150 that is configured for regulating operation of water heater appliance 100. Controller 150 is in, e.g., operative, communication with upper and lower heating elements 118 and 119, compressor 122, tank temperature sensor 130 and ambient temperature sensor 132. Thus, controller 150 may selectively activate upper and lower heating elements 118 and 119 and/or compressor 122 in order to heat water within interior volume 114 of tank 112, e.g., in response to signals from tank temperature sensor 130 and/or ambient temperature sensor 132.

Controller 150 includes memory and one or more processing devices such as microprocessors, CPUs or the like, such as general or special purpose microprocessors operable to execute programming instructions or micro-control code associated with operation of water heater appliance 100. The memory can represent random access memory such as DRAM, or read only memory such as ROM or FLASH. The processor executes programming instructions stored in the memory. The memory can be a separate component from the processor or can be included onboard within the processor. Alternatively, controller 150 may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality instead of relying upon software.

Controller 150 may operate upper heating element 118, lower heating element 119 and/or compressor 122 in order to heat water within interior volume 114 of tank 112. As an example, a user may select or establish a set temperature, t_(s), for water within interior volume 114 of tank 112, or the set temperature t_(s) for water within interior volume 114 of tank 112 may be a default value. Based upon the set temperature t_(s) for water within interior volume 114 of tank 112, controller 150 may selectively activate upper heating element 118, lower heating element 119 and/or compressor 122 in order to heat water within interior volume 114 of tank 112 to the set temperature t_(s) for water within interior volume 114 of tank 112. The set temperature t_(s) for water within interior volume 114 of tank 112 may be any suitable temperature. For example, the set temperature t_(s) for water within interior volume 114 of tank 112 may be between about one hundred degrees Fahrenheit and about one hundred and eighty-degrees Fahrenheit.

FIG. 3 illustrates a method 300 for operating a water heater appliance according to an exemplary embodiment of the present subject matter. Method 300 can be used to operate any suitable water heater appliance. For example, method 300 may be used to operate water heater appliance 100 (FIG. 1). Controller 150 may be programmed or configured to implement method 300. Utilizing method 300, short cycling of sealed system 120, e.g., during a standby mode of water heater appliance 100, may be limited or prevented, as discussed in greater detail below.

The standby operation of water heater appliance 100 may correspond to time periods, such as nighttime or working hours, when a building housing water heater appliance 100 is empty or occupants of the building are not utilizing heated water from water heater appliance 100. Thus, controller 150 may recognize that water heater appliance 100 is in the standby operation of water heater appliance 100 when no water or little water (e.g., less than one gallon per hour) flows out of water heater appliance 100. The flow of heated water out of water heater appliance 100 may be monitored or measured utilizing any suitable method or mechanism in order to assist controller 150 with establishing or determining when to operate water heater appliance 100 in the standby mode. For example, water heater appliance 100 may include a flow meter to monitor the flow rate of heated water out of water heater appliance 100. As another example, water heater appliance 100 may utilize tank temperature sensor 130 to monitor the flow rate of heated water out of water heater appliance 100, e.g., utilizing the method described in U.S. patent application Ser. No. 14/295,800 entitled “A Method for Operating a Water Heater Appliance” of Craig lung-Pei Tsai, which is incorporated by reference herein for all purposes.

At step 310, the set temperature t_(s) of water heater appliance 100 is determined. The set temperature t_(s) for water within interior volume 114 of tank 112 may be established using any suitable method or mechanism at step 310. For example, as discussed above, a user may select or establish the set temperature t_(s) for water within interior volume 114 of tank 112, or the set temperature t_(s) for water within interior volume 114 of tank 112 may be a default value. Method 300 may also include measuring an ambient temperature about water heater appliance 100 at step 310. For example, controller 150 may receive a signal from ambient temperature sensor 132 in order to measure the ambient temperature about water heater appliance 100.

At step 320, a standby recovery temperature, t_(r), for water heater appliance 100 is established. In particular, controller 150 may establish the standby recovery temperature t_(r) for water heater appliance 100 at step 320 based at least in part on the set temperature t_(s) of water heater appliance 100 from step 310 and the ambient temperature, e.g., from ambient temperature sensor 132. The standby recovery temperature t_(r) for water heater appliance 100 may be any suitable temperature. For example, the standby recovery temperature t_(r) may be less than the set temperature t_(s) of water heater appliance 100 at step 320.

As an example, controller 150 may establish the standby recovery temperature t_(r) for water heater appliance 100 as a first standby recovery temperature, t_(r1), for water heater appliance 100 if the set temperature t_(s) of water heater appliance 100 is greater than a threshold set temperature at step 320. Conversely, controller 150 may establish the standby recovery temperature t_(r) for water heater appliance 100 as a second standby recovery temperature t_(r2), for water heater appliance 100 if the set temperature t_(s) of water heater appliance 100 is less than the threshold set temperature at step 320. The threshold set temperature may be any suitable temperature. For example, the threshold set temperature may be about (e.g., within about ten degrees Fahrenheit of) one hundred and thirty degrees Fahrenheit. The first and second standby recovery temperatures t_(r1), t_(r2) may also be any suitable temperatures. For example, the second standby recovery temperature t_(r2) may be greater than the first standby recovery temperature t_(r1). In particular, the second standby recovery temperature t_(r2) may be about (e.g., within four degrees Fahrenheit of) five degrees Fahrenheit greater than the first standby recovery temperature t_(r1).

In addition, the first standby recovery temperature t_(r1) may equal to a difference between the set temperature t_(s) of water heater appliance 100 and a first constant temperature, and the second standby recovery temperature t_(r2) may be equal to a difference between the set temperature t_(s) of water heater appliance 100 and a second constant temperature where the second constant temperature is greater than the first constant temperature. Thus, at step 320, the standby recovery temperature t_(r) for water heater appliance 100 may be established with the following:

t _(r1) =t _(s)−5 if t _(s)<130

t _(r2) =t _(s)−10 if t _(s)≧130

if the ambient temperature measured with ambient temperature sensor 132 is greater than fifty degrees Fahrenheit. Conversely, if the ambient temperature measured with ambient temperature sensor 132 is less than or equal to fifty degrees Fahrenheit, the standby recovery temperature t_(r) for water heater appliance 100 may be established with the following:

t _(r) =t _(s)−5.

As shown above, the first constant temperature may be about (e.g., within about five degrees Fahrenheit of) ten degrees Fahrenheit, and the second constant temperature may about (e.g., within about five degrees Fahrenheit of) five degrees Fahrenheit. In alternative exemplary embodiments, the first and second constant temperatures may be any suitable temperatures.

At step 330, the temperature of water within tank 112 of water heater appliance 100 is measured. As an example, controller 150 may measure or gauge the temperature of water within tank 112 of water heater appliance 100 with tank temperature sensor 130 at step 330. Thus, a temperature measurement from tank temperature sensor 130 may be received at controller 150 during the standby operation of water heater appliance 100 at step 330.

At step 340, controller 150 determines whether the temperature measurement from tank temperature sensor 130 is less than (e.g., or equal to) the standby recovery temperature t_(r) for water heater appliance 100 from step 320. If the temperature measurement from tank temperature sensor 130 is not less than the standby recovery temperature t_(r) for water heater appliance 100, controller 150 continues to monitor the temperature of water within interior volume 114 of tank 112 with tank temperature sensor 130. Conversely, controller 150 activates compressor 122 of sealed system 120 at step 350 if the temperature measurement from tank temperature sensor 130 is less than (e.g., or equal to) the standby recovery temperature t_(r) from step 320 at step 340. Thus, during the standby operation of water heater appliance 100, controller 150 heats water within interior volume 114 of tank 112 with sealed system 120 at step 350 when the temperature measurement from tank temperature sensor 130 is less than (e.g., or equal to) the standby recovery temperature t_(r) from step 320 at step 340.

At step 360, controller 150 determines whether the temperature measurement from tank temperature sensor 130 is greater than (e.g., or equal to) the set temperature t_(s) of water heater appliance 100 from step 310. If the temperature measurement from tank temperature sensor 130 is not greater than the set temperature t_(s) of water heater appliance 100, controller 150 continues to operate sealed system 120 to heat water within interior volume 114 of tank 112 with sealed system 120. Conversely, controller 150 deactivates compressor 122 of sealed system 120 at step 370 if the temperature measurement from tank temperature sensor 130 is greater than (e.g., or equal to) the set temperature t_(s) of water heater appliance 100 at step 360. Thus, controller 150 operates sealed system 120 to heat water within interior volume 114 of tank 112 at steps 350 and 360 until water within interior volume 114 of tank 112 reaches the set temperature t_(s) of water heater appliance 100 at step 360.

By establishing the standby recovery temperature t_(r) for water heater appliance 100 at step 320 based at least in part on the set temperature t_(s) of water heater appliance 100, controller 150 may avoid short cycling sealed system 120 of water heater appliance 100 during standby operations of water heater appliance 100. In particular, controller 150 may permit water within interior volume 114 of tank 112 to cool more when the set temperature t_(s) of water heater appliance 100 is relatively high than when the set temperature t_(s) of water heater appliance 100 is relatively low. When the set temperature t_(s) of water heater appliance 100 is relatively high, a user of water heater appliance 100 may be less likely to notice greater cooling of water within interior volume 114 of tank 112 compared to permitting similar cooling of water within interior volume 114 of tank 112 when the set temperature t_(s) of water heater appliance 100 is relatively low. Thus, controller 150 may activate sealed system 120 less frequently and avoid short cycling of sealed system 120 during standby operations of water heater appliance 100 when the set temperature t_(s) of water heater appliance 100 is relatively high compared to when the set temperature t_(s) of water heater appliance 100 is relatively low utilizing method 300. In such a manner, method 300 may also assist with increasing an efficiency of water heater appliance 100. Similarly, by establishing the standby recovery temperature t_(r) for water heater appliance 100 at step 320 based at least in part on the ambient temperature about water heater appliance 100, an efficiency of water heater appliance 100 may be improved. As will be understood by those skilled in the art, the heat pump capacity of sealed system 120 decreases as the ambient temperature decreases, and heat pump capacity of sealed system 120 increases as the ambient temperature increases. Thus, short cycling of sealed system 120 may be less frequent when the ambient temperature is relatively low because it takes longer to heat water with sealed system 120 in such conditions. In addition, heated water from water heater appliance 100 is generally mixed with cold water by a user at a downstream usage point, such as a shower, faucet, etc., in order to cool the heated water to a suitable temperature. When the ambient temperature is relatively low, the cold water may be colder compared to when the ambient temperature is relatively high. Thus, more hot water from water heater appliance 100 may be needed to provide water at the suitable temperature when the ambient temperature is relatively low, and decreasing the standby recovery temperature t_(r) in such conditions may provide less heated water downstream.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A method for operating a heat pump water heater appliance, comprising: determining a set temperature of the heat pump water heater appliance; measuring an ambient temperature about the heat pump water heater appliance with an ambient temperature sensor of the heat pump water heater appliance; establishing a standby recovery temperature for the heat pump water heater appliance based at least in part on the set temperature of the heat pump water heater appliance and the ambient temperature about the heat pump water heater appliance; receiving a temperature measurement from a tank temperature sensor of the heat pump water heater appliance during a standby operation of the heat pump water heater appliance; and activating a sealed system of the heat pump water heater appliance if the temperature measurement from the tank temperature sensor is less than the standby recovery temperature at said step of receiving.
 2. The method of claim 1, wherein said step of establishing comprises: establishing a first standby recovery temperature for the heat pump water heater appliance if the set temperature of the heat pump water heater appliance is greater than a threshold set temperature; and establishing a second standby recovery temperature for the heat pump water heater appliance if the set temperature of the heat pump water heater appliance is less than the threshold set temperature, the second standby recovery temperature being greater than the first standby recovery temperature.
 3. The method of claim 2, wherein the threshold set temperature is about one hundred and thirty degrees Fahrenheit.
 4. The method of claim 3, wherein the first standby recovery temperature is equal to a difference between the set temperature of the heat pump water heater appliance and a first constant temperature, the second standby recovery temperature being equal to a difference between the set temperature of the heat pump water heater appliance and a second constant temperature.
 5. The method of claim 4, wherein the first constant temperature is about ten degrees Fahrenheit and the second constant temperature is about five degrees Fahrenheit.
 6. The method of claim 2, wherein the second standby recovery temperature is about five degrees Fahrenheit greater than the first standby recovery temperature.
 7. The method of claim 1, wherein the standby recovery temperature is less than the set temperature of the heat pump water heater appliance.
 8. The method of claim 1, further comprising deactivating the sealed system of the heat pump water heater appliance when the temperature measurement from the tank temperature sensor is the set temperature of the heat pump water heater appliance after said step of activating.
 9. The method of claim 1, wherein no water flows out of the heat pump water heater appliance during the standby operation of the heat pump water heater appliance.
 10. The method of claim 1, wherein said step of activating comprises activating a compressor of the sealed system.
 11. A heat pump water heater appliance, comprising: a tank defining an interior volume; an ambient temperature sensor; a tank temperature sensor positioned at the tank and configured for measuring a temperature of water within the interior volume of the tank; a sealed system operable to heat water within the interior volume of the tank, the sealed system having a compressor; and a controller in operative communication with the ambient temperature sensor, the tank temperature sensor and the compressor of the sealed system, the controller configured for measuring an ambient temperature with the ambient temperature sensor; establishing a standby recovery temperature based at least in part on a set temperature and the ambient temperature; receiving a temperature measurement from the tank temperature sensor during a standby operation; and activating the compressor of the sealed system if the temperature measurement from the tank temperature sensor is less than the standby recovery temperature at said step of receiving.
 12. The heat pump water heater appliance of claim 11, wherein said step of establishing comprises: establishing a first standby recovery temperature if the set temperature is greater than a threshold set temperature; and establishing a second standby recovery temperature if the set temperature is less than the threshold set temperature, the second standby recovery temperature being greater than the first standby recovery temperature.
 13. The heat pump water heater appliance of claim 12, wherein the threshold set temperature is about one hundred and thirty degrees Fahrenheit.
 14. The heat pump water heater appliance of claim 13, wherein the first standby recovery temperature is equal to a difference between the set temperature and a first constant temperature, the second standby recovery temperature being equal to a difference between the set temperature and a second constant temperature.
 15. The heat pump water heater appliance of claim 14, wherein the first constant temperature is about ten degrees Fahrenheit and the second constant temperature is about five degrees Fahrenheit.
 16. The heat pump water heater appliance of claim 11, wherein the controller is further configured for deactivating the compressor of the sealed system when the temperature measurement from the tank temperature sensor is the set temperature of the heat pump water heater appliance after said step of activating.
 17. The heat pump water heater appliance of claim 11, wherein the standby recovery temperature is less than the set temperature.
 18. The heat pump water heater appliance of claim 11, wherein no water flows out of the tank during the standby operation.
 19. The heat pump water heater appliance of claim 11, wherein the tank temperature sensor is the only temperature sensor positioned at the tank and configured for measuring the temperature of water within the interior volume of the tank. 